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Date: Wed, 2 Mar 2016 15:09:35 -0500 From: Chris Metcalf <cmetcalf@...hip.com> To: Gilad Ben Yossef <giladb@...hip.com>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, "Rik van Riel" <riel@...hat.com>, Tejun Heo <tj@...nel.org>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Christoph Lameter <cl@...ux.com>, Viresh Kumar <viresh.kumar@...aro.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Andy Lutomirski <luto@...capital.net>, Mark Rutland <mark.rutland@....com>, <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org> CC: Chris Metcalf <cmetcalf@...hip.com> Subject: [PATCH v10 11/12] arm64: factor work_pending state machine to C Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc state machine that can be difficult to reason about due to duplicated code and a large number of branch targets. This patch factors the common logic out into the existing do_notify_resume function, converting the code to C in the process, making the code more legible. This patch tries to closely mirror the existing behaviour while using the usual C control flow primitives. As local_irq_{disable,enable} may be instrumented, we balance exception entry (where we will almost most likely enable IRQs) with a call to trace_hardirqs_on just before the return to userspace. Signed-off-by: Chris Metcalf <cmetcalf@...hip.com> --- arch/arm64/kernel/entry.S | 12 ++++-------- arch/arm64/kernel/signal.c | 30 ++++++++++++++++++++++-------- 2 files changed, 26 insertions(+), 16 deletions(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 1f7f5a2b61bf..966d0d4308f2 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -674,18 +674,13 @@ ret_fast_syscall_trace: * Ok, we need to do extra processing, enter the slow path. */ work_pending: - tbnz x1, #TIF_NEED_RESCHED, work_resched - /* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */ mov x0, sp // 'regs' - enable_irq // enable interrupts for do_notify_resume() bl do_notify_resume - b ret_to_user -work_resched: #ifdef CONFIG_TRACE_IRQFLAGS - bl trace_hardirqs_off // the IRQs are off here, inform the tracing code + bl trace_hardirqs_on // enabled while in userspace #endif - bl schedule - + ldr x1, [tsk, #TI_FLAGS] // re-check for single-step + b finish_ret_to_user /* * "slow" syscall return path. */ @@ -694,6 +689,7 @@ ret_to_user: ldr x1, [tsk, #TI_FLAGS] and x2, x1, #_TIF_WORK_MASK cbnz x2, work_pending +finish_ret_to_user: enable_step_tsk x1, x2 kernel_exit 0 ENDPROC(ret_to_user) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index e18c48cb6db1..3432e14b7d6e 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -402,15 +402,29 @@ static void do_signal(struct pt_regs *regs) asmlinkage void do_notify_resume(struct pt_regs *regs, unsigned int thread_flags) { - if (thread_flags & _TIF_SIGPENDING) - do_signal(regs); + while (true) { - if (thread_flags & _TIF_NOTIFY_RESUME) { - clear_thread_flag(TIF_NOTIFY_RESUME); - tracehook_notify_resume(regs); - } + if (thread_flags & _TIF_NEED_RESCHED) { + schedule(); + } else { + local_irq_enable(); + + if (thread_flags & _TIF_SIGPENDING) + do_signal(regs); - if (thread_flags & _TIF_FOREIGN_FPSTATE) - fpsimd_restore_current_state(); + if (thread_flags & _TIF_NOTIFY_RESUME) { + clear_thread_flag(TIF_NOTIFY_RESUME); + tracehook_notify_resume(regs); + } + + if (thread_flags & _TIF_FOREIGN_FPSTATE) + fpsimd_restore_current_state(); + } + local_irq_disable(); + + thread_flags = READ_ONCE(current_thread_info()->flags); + if (!(thread_flags & _TIF_WORK_MASK)) + break; + } } -- 2.1.2
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